//定义画布宽高和生成点的个数
var WIDTH = window.innerWidth, HEIGHT = window.innerHeight, POINT = 35;

var canvas = document.getElementById('Mycanvas');
canvas.width = WIDTH,
canvas.height = HEIGHT;
var context = canvas.getContext('2d');
context.strokeStyle = 'rgba(0,0,0,0.02)',
context.strokeWidth = 1,
context.fillStyle = 'rgba(0,0,0,0.05)';
var circleArr = [];

//线条：开始xy坐标，结束xy坐标，线条透明度
function Line (x, y, _x, _y, o) {
	this.beginX = x,
	this.beginY = y,
	this.closeX = _x,
	this.closeY = _y,
	this.o = o;
}
//点：圆心xy坐标，半径，每帧移动xy的距离
function Circle (x, y, r, moveX, moveY) {
	this.x = x,
	this.y = y,
	this.r = r,
	this.moveX = moveX,
	this.moveY = moveY;
}
//生成max和min之间的随机数
function num (max, _min) {
	var min = arguments[1] || 0;
	return Math.floor(Math.random()*(max-min+1)+min);
}
// 绘制原点
function drawCricle (cxt, x, y, r, moveX, moveY) {
	var circle = new Circle(x, y, r, moveX, moveY)
	cxt.beginPath()
	cxt.arc(circle.x, circle.y, circle.r, 0, 2*Math.PI)
	cxt.closePath()
	cxt.fill();
	return circle;
}
//绘制线条
function drawLine (cxt, x, y, _x, _y, o) {
	var line = new Line(x, y, _x, _y, o)
	cxt.beginPath()
	cxt.strokeStyle = 'rgba(0,0,0,'+ o +')'
	cxt.moveTo(line.beginX, line.beginY)
	cxt.lineTo(line.closeX, line.closeY)
	cxt.closePath()
	cxt.stroke();

}
//初始化生成原点
function init () {
	circleArr = [];
	for (var i = 0; i < POINT; i++) {
		circleArr.push(drawCricle(context, num(WIDTH), num(HEIGHT), num(15, 2), num(10, -10)/40, num(10, -10)/40));
	}
	draw();
}

//每帧绘制
function draw () {
	context.clearRect(0,0,canvas.width, canvas.height);
	for (var i = 0; i < POINT; i++) {
		drawCricle(context, circleArr[i].x, circleArr[i].y, circleArr[i].r);
	}
	for (var i = 0; i < POINT; i++) {
		for (var j = 0; j < POINT; j++) {
			if (i + j < POINT) {
				var A = Math.abs(circleArr[i+j].x - circleArr[i].x),
					B = Math.abs(circleArr[i+j].y - circleArr[i].y);
				var lineLength = Math.sqrt(A*A + B*B);
				var C = 1/lineLength*7-0.009;
				var lineOpacity = C > 0.03 ? 0.03 : C;
				if (lineOpacity > 0) {
					drawLine(context, circleArr[i].x, circleArr[i].y, circleArr[i+j].x, circleArr[i+j].y, lineOpacity);
				}
			}
		}
	}
}

//调用执行
window.onload = function () {
	init();
	setInterval(function () {
		for (var i = 0; i < POINT; i++) {
			var cir = circleArr[i];
			cir.x += cir.moveX;
			cir.y += cir.moveY;
			if (cir.x > WIDTH) cir.x = 0;
			else if (cir.x < 0) cir.x = WIDTH;
			if (cir.y > HEIGHT) cir.y = 0;
			else if (cir.y < 0) cir.y = HEIGHT;
			
		}
		draw();
	}, 16);
}